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UNITED STATES PUBLIC HEALTH SERVICE 

EXPERIMENTAL 

INSECT TRANSMISSION OF 

ANTHRAX 

BY 

M. BRUIN MITZMAIN 

Veterinary Entomologist 
Government of the Philippines 



REPRINT No. 162 

FROM THE 

PUBLIC HEALTH REPORTS 

JaxUARY 9, 1914 




WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1914 



l^'vno^r-nr. 






EXPERIMENTAL INSECT TRANSMISSION OF ANTHRAX.' 

By M. Bruin Mitzmain, Veterinary Entomologist, Government of tlie Philippines. 

Only a very few clearly defined instances have been recorded of 
any experimental evidence demonstrating the r61e of suctorial insects 
in the dissemination of anthrax. It was with this in view that the 
writer investigated the purely entomological aspects of the anthi'ax 
problem. The question of contamination tlirough skin abrasions 
produced by insects other than the blood-sucking forms is not at 
present considered. 

Tliis preliminary note is the culmination of a great number of 
experiments attempted. Only the three positive ones are cited in 
detail. The difficulty presented is essentially in that the problem 
of anthrax dissemination is not significant for the suctorial insect 
until the peripheral circulation becomes invaded wdth tremendous 
numbers of the antlirax bacterium. In the first trials the blood 
donors were employed 24 hours to 3 days prior to their death, and 
although characteristic cultures were obtained from blood drawn 
from the ear upon these occasions, no transfer of infection tlu-ough 
fly biting resulted in the many experiments attempted. 

Only negative results were obtained when it was aimed to demon- 
strate the possibility of biting fly transmission with animals recently 
dead of the disease. Both Stomoxys calcitrans and Tahanus striatus 
were employed in six experiments in the direct method. The 
primary host in these instances was used 10 minutes after death. A 
pure culture of antlirax was obtained during the experiments from 
the skin in the mucous layer of the region where the fhes were 
applied. 

The experiments resulting in the transmission of the anthrax 
organism were tried with an artificially infected guinea pig, which 
died of the disease upon the tliird day. The flies were appHed two 
and one-half hours to a few minutes before the death of the blood 
donor. Guinea pigs were used to receive the infective bites of 
Stomoxys calcitrans and Tabanus striatus. Each animal was placed 
in a gauze sack strapped to an individual board and the fhes were 
induced to feed when appued from separate test tubes. Stomoxys 
calcitrans was used as the porter in two experiments and Tahanus 
striatus in a single experiment. With both species the infection was 
successfully transferred by the direct method in which the flies were 

I Reprint from the Public Health Reports, vol. 20, No. 2, Jan. 9, 1914. 
. .2 

24942°— 14 [), OP (j, 

FEB 8 .1914 



■->" INSECT TKANSMISSION OF ANTHRAX. 3 

"4^.'^ interrupted while feeding on the sick animal. The stable flies were 

^ transferred to the healthy animal in one trial with only a few seconds' 

J interval after biting the infected host, and in the other instance an 

interval of 10 minutes elapsed between the feedings. A total of 

.-^> 20 flies were used in the first experiment and 30 flies in the second 

'"" trial. 

The exposed animals died in both cases during the evening of the 
third day. Typical pictures of anthrax infection were presented at 
the necropsy of the two animals. In addition a substantial gelati- 
nous and hemorrhagic oedema was observed in the subcutaneous 
region of the area upon which the flies were aj^plied in biting. The 
spleens of both animals yielded characteristic square-ended rods, 
which showed typical picture when tested with McFadyean's differ- 
ential stain. Pure cultures were obtained from the spleens of the 
dead animals. The growth on agar resembled that of the initial 
pure culture, and spores produced on a potato medium stained 
quite typically. The agar cultures when injected reproduced the 
disease with fatal results in guinea pigs used in later experiments. 

Similar results were obtained in all essentials when horseflies were 
employed to transfer the disease from the sick to a healthy guinea 
pig. Three flies were used to carry the infection, with only a few 
seconds' interval from infected to healthy host. The latter died on 
the fourth day after the flies were applied. The autopsy was made 
a few mmutes after death. As m the other instances, there was no 
rigor mortis. The site of fly biting was not much involved; only a 
slight gelatinous hemorrhagic oedema. The subcutaneous injection 
also was slight. The spleen was greatly enlarged and extremely 
friable. Stained smears from this organ showed characteristic 
square-ended rods in great numbers. McFadyean's differential test 
was very distinct. Numerous nonmotUe rods were seen in a hang- 
ing di'op taken from the heart's blood. 

Vigorous growth characteristic of the anthrax bacterium was 
obtained on agar, and later the disease was reproduced in a horse 
from a saline suspension of the agar culture. 

Typical organisms were seen in the feces of horseflies at various 
intervals up to 48 hours from the time the infected animal was 
bitten. The accumulated deposits of 3 tabanids, 2 to 3 days after 
the mfective bites, were injected in a saline suspension into a healthy 
gumea pig, which died of typical anthrax 4 days later. An agar 
culture from the spleen of this animal showed typical growth, and a 
microscopical verification of the character of the organism was 
obtained. 

The feces of the stable fly were likewise found to be infected up to 
24 hours after obtaming blood from a sick animal. A nearly pure 
culture of anthrax was obtained from the droppings of 2 flies fed 24 



4 INSECT TKANSMISSION OF ANTHRAX. 

hours previously on infected material. A mixed culture showing 
numerous typical rods was obtained from the gut contents of 3 stable 
flies which were killed 24 hours after biting a sick animal. 

A series of experiments is at present being conducted with anthrax 
in cattle and horses. Guinea pigs or other rodents will in every 
instance be employed as blood donors, as experience has shown that 
it is difficult in large animals to time the probable invasion of the 
peripheral circulation by the anthrax organisms so as to render 
insect transmission practicable. An attempt will be made to deter- 
mine the limits of infection in flies acting as carriers of contaminative 
material. 

Editor's Note. — Tlie following message from Manila was received December 31, 
1913: 

"Antlirax transmission experiments verified Stomoxys calcitrans 20 minutes interval 
harbors bacilli in feces 14 to 17 days inclusive in the stomach 19 days cultures positive 
Tabanus striatus biting direct bacilli in feces 10 days. 

"MiTZMAIN." 

o 



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